Oil pumping system using a switched reluctance motor to drive a screw pump

ABSTRACT

An oil-pumping system includes a pumping-well unit, a controller composed of a main control circuit, a power converter, a current sensor and a position sensor, a switched reluctance motor mounted at the pumping-well unit and electrically coupled to the controller, a casing connected to the pumping-well unit, an oil suction pipe mounted in the casing, a pumping rod disposed in the oil suction pipe and connected to the switched reluctance motor, and a screw pump connected to the pumping rod in the oil suction pipe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to oil production technology and more particularly, to an oil pumping system for the production of crude oil by using a switched reluctance motor to drive a screw pump.

2. Description of the Related Art

Conventionally, two different types of motor drives, namely, the indirect drive type and the direct drive type, are selectively used for the production of crude oil. An indirect type motor drive uses a motor to rotate a reduction gear box through a transmission belt, thereby driving an oil pump to pump crude oil. This indirect type motor drive has numerous drawbacks. The transmission of the transmission belt and the reduction gear box consumes much power, or about 20% of totally consumed power. Further, the transmission belt and the reduction gear box wear quickly with use, and the components thereof must be regularly examined and replaced. A direct type motor drive uses a permanent magnet motor to drive an oil pump directly. Due to direct driving, less power is consumed. However, as the production of a permanent magnet motor uses rare earth magnetic steel, its manufacturing cost is high. Further, a permanent magnet motor may fail under a high temperature environment. Further, the output torque of a permanent magnet motor is limited.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide an oil pumping system, which uses a switched reluctance motor to drive a screw pump, facilitating speed control, reducing power consumption, achieving the effects of high torque, low starting current and non-wearing, and avoiding demagnetization failure.

To achieve this and other objects of the present invention, an oil pumping system comprises a pumping-well unit, a controller, a switched reluctance motor mounted at the pumping-well unit and electrically coupled to the controller, a casing connected to the pumping-well unit, an oil suction pipe mounted in the casing, a pumping rod disposed in the oil suction pipe and connected to the switched reluctance motor, and a screw pump connected to the pumping rod in the oil suction pipe. The controller comprises a main control circuit, a power converter, a current sensor and a position sensor. The position sensor and the current sensor are adapted to detect power on/off status of each winding pole of the stator. The main control circuit receives and analyzes sensing signals indicative of power on/off status of the winding poles of the stator provided by the position sensor and the current sensor, and provides a corresponding control signal to power on/off the winding poles of the stator. The power converter converts the control signal provided by the main control circuit into a power signal for driving the switched reluctance motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating an oil pumping system in accordance with the present invention.

FIG. 2 is a system block diagram of the oil pumping system in accordance with the present invention.

FIG. 3 is a cross sectional view of the switched reluctance motor, illustrating pole B of motor stator conducted and pole A powered off.

FIG. 4 is a cross sectional view of the switched reluctance motor, illustrating pole C of motor stator conducted and pole B powered off.

FIG. 5 is a cross sectional view of the switched reluctance motor, illustrating pole D of motor stator conducted and pole C powered off.

FIG. 6 is a cross sectional view of the switched reluctance motor, illustrating pole A of motor stator conducted and pole D powered off.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-6, an oil pumping system in accordance with the present invention is shown comprising a pumping-well unit 30, a switched reluctance motor 20 mounted at the top side of the pumping-well unit 30 and electrically coupled to a controller 10, a casing 11 connected to the bottom side of the pumping-well unit 30, an oil suction pipe 12 mounted in the casing 11, a pumping rod 13 disposed in the oil suction pipe 12 and connected to the switched reluctance motor 20, and a screw pump 14 connected to the bottom end of the pumping rod 13 in the oil suction pipe 12. The switched reluctance motor 20 comprises a shaft 21 connected to the pumping rod 13 and the screw pump 14 in the oil suction pipe 12, a stator 22, a rotor 23 fixedly mounted at the shaft 21 and surrounded by the stator 22. The stator 22 comprises a plurality of winding poles (A,A′), (B,B′), (C,C′) and (D,D′) for generating a magnetic attractive force when electrically conducted. The rotor 23 comprises a plurality of rotor teeth (E,E′), (F,F′) and (G,G′). When the winding poles of the stator 22 are electrically conducted, a magnetic attractive force is produced to attract the rotor teeth of the rotor 23, causing the position of the rotor teeth to be shifted. The controller 10 comprises a main control circuit, a power converter, a current sensor, a position sensor. The position sensor and the current sensor can detect the power on/off status of each winding pole of the stator 22 of the switched reluctance motor 20. The main control circuit receives and analyzes sensing signals (indicative of power on/off status of the winding poles of the stator) provided by the position sensor and the current sensor, and provides a corresponding control signal to conduct or to cut off power supply from the winding poles of the stator 22. The power converter converts the control signal provided by the main control circuit into a power signal for driving the switched reluctance motor 20.

The operation and effects of the present invention are outlined hereinafter with reference to FIGS. 3, 4, 5 and 6. As illustrated in FIG. 3, the controller controls the winding poles (B,B′) of the stator 22 to be electrically conducted to generate a magnetic attractive force (magnetic line of force always seeks the shortest path of least resistance) to attract the rotor teeth (F,F′) of the rotor 23. At this time, the winding poles (A,A′) of the stator 22 are kept in line with the rotor teeth (E,E′) of the rotor 23; the controller 10 controls the winding poles (A,A′) of the stator 22 to be off, and therefore, the rotor teeth (E,E′) of the rotor 23 are not attracted, allowing the rotor teeth (F,F′) of the rotor 23 to be attracted in shifting the phase of the rotor 23. Thereafter, as shown in FIG. 4, the controller electrically conducts the winding poles (C,C′) of the stator 22 to attract the rotor teeth (G,G′) of the rotor 23 and simultaneously electrically cuts off power supply from the winding poles (B,B′) of the stator 22 to release the rotor teeth (F,F′) of the rotor 23, and therefore the rotor 23 is rotated further. Thereafter, as shown in FIG. 5, the controller electrically conducts the winding poles (D,D′) of the stator 22 to attract the rotor teeth (E,E′) of the rotor 23 and simultaneously electrically cuts off power supply from the winding poles (C,C′) of the stator 22 to release the rotor teeth (G,G′) of the rotor 23, and therefore the rotor 23 is rotated further. Thereafter, as shown in FIG. 6, the controller electrically conducts the winding poles (A,A′) of the stator 22 to attract the rotor teeth (F,F′) of the rotor 23 and simultaneously electrically cuts off power supply from the winding poles (D,D′) of the stator 22 to release the rotor teeth (E,E′) of the rotor 23. The aforesaid procedure is repeated again and again, causing the rotor 23 to continuously rotate the shaft 21 and the screw pump 14 in pumping crude oil into an oil delivery pipe 31 for output.

As stated above, by means of switched reluctance drive to rotate the rotor 23, the invention achieves the advantages of: (1) speed control is conveniently achieved by means of changing the power on/off frequency of the winding poles of the stator; (2) when going to stop the system, controls the magnetic attractive force to attract the rotor, and the rotor is stopped accurately, i.e., the invention achieves accurate and stable braking effects; (3) by means of magnetic attractive force to rotate the rotor, a high torque is achieved, and therefore the invention achieves the effects of high torque, low starting current and non-wearing; (4) the switched reluctance motor of the invention eliminates the use of rare earth magnetic steel, saving the cost and avoiding rare earth demagnetization failure; (5) the direct drive design of the invention eliminates the power consumption drawback of a belt or gear transmission design.

Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims. 

What the invention claimed is:
 1. An oil-pumping system, comprising: a pumping-well unit, a controller, a switched reluctance motor mounted at a top side of said pumping-well unit and electrically coupled to said controller, a casing connected to a bottom side of said pumping-well unit, an oil suction pipe mounted in said casing, a pumping rod disposed in said oil suction pipe and connected to said switched reluctance motor, and a screw pump connected to a bottom end of said pumping rod in said oil suction pipe, said switched reluctance motor comprising a shaft connected to said pumping rod in said oil suction pipe, a stator, a rotor fixedly mounted at said shaft and surrounded by said stator, said stator comprising a plurality of winding poles respectively electrically conductable for generating a magnetic attractive force subject to the control of said controller, said rotor comprising a plurality of rotor teeth attractable by the magnetic attractive force generated by said winding poles, said controller comprising a main control circuit, a power converter, a current sensor and a position sensor, said position sensor and said current sensor being adapted to detect power on/off status of each said winding pole of said stator of said switched reluctance motor, said main control circuit receiving and analyzing sensing signals indicative of power on/off status of said winding poles of said stator provided by said position sensor and said current sensor and providing a corresponding control signal to power on/off said winding poles of said stator, said power converter converting the control signal provided by said main control circuit into a power signal for driving said switched reluctance motor. 